Method for fabricating etch mask and patterning process using the same

ABSTRACT

A method for fabricating a mask is provided. A patterned sacrificial layer is formed over a mask material layer, and the patterned sacrificial layer has an etch selectivity different from that of the mask material layer. An isotropic etch process is performed to the mask material layer by using the patterned sacrificial layer as an etch mask to form a mask layer, wherein the dimension of the mask layer is smaller than that of the patterned sacrificial layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor process, and more particularly to a method for fabricating a mask and a patterning process using the mask.

2. Description of the Related Art

As the integration of circuits continues to increase, the dimensions of circuit devices must shrink to meet the requirement. One of the most important processes in the semiconductor technology is the photolithographic process. Patterns of different film layers and areas with dopants of Metal-Oxide-Semiconductor (MOS) devices are defined by the photolithographic process. In detail, dimensions of a photoresist layer formed by the photolithographic process or dimensions of a mask formed by using the patterned photoresist layer are closely related to the photolithographic process. Whether the device integration of the semiconductor technology can progress to smaller dimensions is depended upon the development of the photolithographic technology.

In order to shrink the dimensions of a device and improve exposure resolution, various improved designs of masks or light sources with shorter wavelengths have been used to obtain devices with smaller dimensions. Regardless of the improvement methods, the improvement of the device dimensions is restricted by the limitation of the exposure equipment. For example, the exposure equipment itself has an ultimate resolution. The dimension of the defined photoresist layer can only be reduced to a specific dimension, i.e., the critical dimension (CD), and cannot be further reduced. Accordingly, to further decrease the dimension of a film layer defined by using the photoresist layer is also limited.

The issue described above can be solved by treating the patterned photoresist layer with the trim technology to reduce the dimension of the patterned photoresist layer. However, the dimension of a trimmed photoresist layer is so small that photoresist layer may collapse because the trimmed photoresist layer cannot withstand stand the stress induced in the subsequent etch process. As a result, the accuracy of the dimension of the film layer defined by the trimmed photoresist layer is affected.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method for fabricating a mask with a dimension smaller than the critical dimension (CD) of the photolithographic process.

The present invention is also directed to a patterning process to overcome the restraint on size reduction of devices due to the limitation of the traditional exposure equipment.

The present invention provides a method for fabricating a mask. The method includes forming a patterned sacrificial layer over a mask material layer. The patterned sacrificial layer has an etch selectivity different from that of the mask material layer. An isotropic etch process is performed to the mask material layer to form a mask layer by using the patterned sacrificial layer as an etch mask. A dimension of the mask layer is smaller than a dimension of the patterned sacrificial layer.

The present invention provides a patterning process. The process includes forming a mask material layer over a material layer. The mask material layer has an etch selectivity different from that of the material layer. A patterned sacrificial layer is formed over the mask material layer. The patterned sacrificial layer has an etch selectivity different from that of the mask material layer. The patterned sacrificial layer has an etch selectivity the same as, or different from, that of the material layer. An isotropic etch process is performed to the mask material layer to form a mask layer by using the patterned sacrificial layer as an etch mask. A dimension of the mask layer is smaller than a dimension of the patterned sacrificial layer. The material layer is then etched by using the mask layer as an etch mask.

According to the method for fabricating a mask or the patterning process of embodiments of the present invention, the method for forming the patterned sacrificial layer forms a sacrificial layer over the mask material layer. A patterned photoresist layer is then formed over the sacrificial layer. The sacrificial layer is etched by using the patterned photoresist layer as an etch mask, wherein, the patterned photoresist layer has a critical dimension (CD), and the dimension of the mask layer is smaller than the CD.

According to the method for fabricating a mask or the patterning process of embodiments of the present invention, the isotropic etch process comprises a wet etch process, for example.

According to the method for fabricating a mask or the patterning process of the embodiments of the present invention, the material of the mask material layer comprises, for example, silicon oxide, silicon nitride, silicon oxynitride, polysilicon, doped polysilicon or a metal material.

According to the method for fabricating a mask or the patterning process of the embodiments of the present invention, the material of the patterned sacrificial layer comprises, for example, silicon oxide, silicon nitride, silicon oxynitride, polysilicon, doped polysilicon or a metal material.

According to the patterning process of an embodiment of the present invention, the material of the material layer comprises silicon oxide, silicon nitride, silicon oxynitride, polysilicon, doped polysilicon or a metal material.

The present invention uses the patterned sacrificial layer to define the film as the actual mask. By using the isotropic etch process, the dimension of the film can be further reduced. Accordingly, the dimension of the mask layer is smaller than that of the sacrificial layer. In other words, if the dimension of the patterned sacrificial layer is the smallest dimension (critical dimension) that can be produced by the photolithographic equipment, the dimension of the mask layer is smaller than the critical dimension. Accordingly, the mask layer can be used to fabricate devices with smaller dimensions. The integration of devices is thus improved.

The above and other features of the present invention will be better understood from the following detailed description of the preferred embodiments of the invention that is provided in communication with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D are schematic cross sectional views showing the progression of a patterning process according to an embodiment of the present invention.

DESCRIPTION OF SOME EMBODIMENTS

FIGS. 1A-1D are schematic cross sectional views showing the progression of a patterning process according to an embodiment of the present invention.

Referring to FIG. 1A, a mask material layer 104 is formed over a material layer 102. The mask material layer 104 has an etch selectivity different from that of the material layer 102, wherein, the material layer 102 is formed over a substrate 100, for example. The material of the material layer 102 can be, for example, silicon oxide, silicon nitride, silicon oxynitride, polysilicon, doped polysilicon or a metal material. If the material layer 102 serves as a gate after subsequent patterning processes, a gate dielectric layer 106 can further be formed between the material layer 102 and the substrate 100. In addition, the material of the mask material layer 104 can be, for example, silicon oxide, silicon nitride, silicon oxynitride, polysilicon, doped polysilicon or a metal material. The material of the mask material layer 104 is not specific as long as the mask material layer 104 has an etch selectivity different from that of the material layer 102.

A patterned sacrificial layer 108 is then formed over the mask material layer 104. The patterned sacrificial layer 108 has an etch selectivity different from that of the mask material layer 104. The patterned sacrificial layer 108 has an etch selectivity the same as, or different from, that of the material layer 102, wherein, the material of the patterned sacrificial layer 108 can be, for example, silicon oxide, silicon nitride, silicon oxynitride, polysilicon, doped polysilicon or a metal material. SThe material of the patterned sacrificial layer 108 is not specific, as long as the patterned sacrificial layer 108 has an etch selectivity different from that of the mask material layer 104. In other words, the patterned sacrificial layer 108 and the material layer 102 can be the same, or different, materials.

In addition, the method of forming the patterned sacrificial layer 108, for example, includes forming a sacrificial material layer (not shown) over the mask material layer 104. Then a patterned photoresist layer 110 is formed over the sacrificial material layer 108, in which an exposure process is performed to a photoresist layer (not shown) by using the mask 112, and a development process is performed to the photoresist layer to form the patterned photoresist layer 110. By using the patterned photoresist layer 110 as an etch mask, the sacrificial material layer is etched to form the patterned sacrificial layer 108. In an embodiment, the patterned photoresist layer 110 has a critical dimension due to the limitation of the exposure equipment. The patterned sacrificial layer 108 defined by using the patterned photoresist layer 110 also has the same critical dimension.

Referring to FIG. 1B, by using the patterned sacrificial layer 108 as an etch mask, an isotropic etch process is performed to the mask material layer 104 to form the mask layer 104 a. The dimension of the mask layer 104 a is smaller than that of the patterned sacrificial layer 108. The isotropic etch process can be a wet etch process, for example. Because the patterned sacrificial layer 108 has an etch selectivity different from that of the patterned material layer 104, the patterned sacrificial layer 108 can withstand the etch process. It should be noted that because the etch process is an isotropic etch process, portions of the mask material laeyr 104 are removed to form undercuts on the mask material layer 104 under the patterned sacrificial layer 108. The dimension of the mask layer 104 a is smaller than that of the patterned sacrificial layer 108. In addition, during the process of etching the mask material layer 104, the patterned photoresist layer 110 and the patterned sacrificial layer 108 serve as an etch mask. In another embodiment, the patterned photoresist layer 110 is removed first, and then the patterned sacrificial layer 108 serves as an etch mask in the etch process for the mask material layer 104.

Referring to FIGS. 1C and 1D, the material layer 102 is etched by using the mask layer 104 a as an etch mask. FIG. 1C is a cross sectional view of the structure during the etch process. FIG. 1D is a cross sectional view of the structure after the etch process. In FIG. 1C, the patterned sacrificial layer 108 with a larger dimension covers a portion of the material layer 102 at the initial step of the etch process. If the patterned sacrificial layer 108 serves as an etch mask, the extrusion portion 114 of the defined material layer 102 a is larger than the mask layer 104 a. However, when the etch process is performed for a period of time as shown in FIG. 1D, the patterned sacrificial layer 108 is gradually removed and the mask layer 104 a is exposed. Then the mask layer 104 a serves as the etch mask so that the dimension of the mask layer 102 b is equal to the dimension of the mask layer 104 a. The dimension of the material layer 102 b is thus smaller than the critical dimension.

In addition, the mask layer 104 a has an etch selectivity different from that of the material layer 102. The mask layer 104 effectively prevents the material layer 102 from being etched. Accordingly, the dimension of the defined material layer 102 b is more accurate.

Accordingly, the present invention uses the patterned sacrificial layer to define the film which is to be as the a mask. By using the isotropic etch process, the dimension of the mask can be further reduced. Accordingly, the dimension of the mask layer is smaller than that of the sacrificial layer. In other words, if the dimension of the patterned sacrificial layer is the smallest dimension (critical dimension) which can be obtained by the photolithographic equipment, the dimension of the mask layer is smaller than the critical dimension. Accordingly, the mask layer can be used to fabricate devices with smaller dimensions. The integration of devices is thus improved.

In addition, the present invention uses the isotropic etch process to reduce the dimension of the mask layer so that the dimension of the photoresist layer used to define the sacrificial layer need not be reduced. Accordingly, the collapse of the photoresist layer as often occurs in the prior art technology is prevneted. Further, the dimension of the defined layer is more accurate.

In addition, the present invention uses the patterned sacrificial layer, the mask material layer and the material layer with different etch selectivity ratios during the etch process. The film layer serving as an etch mask can thus effectively withstand the etch process. Accordingly, the dimension of the defined layer is more accurate.

In addition, though the etch process is performed by using the mask layer formed according to the embodiment of the present, the application of the present invention, however, is not limited thereto. In short, the mask of the present invention can also be used in an ion implantation process or other processes which require the mask.

Although the present invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be constructed broadly to include other variants and embodiments of the invention which may be made by those skilled in the field of this art without departing from the scope and range of equivalents of the invention. 

1. A method for fabricating a mask, comprising: forming a patterned sacrificial layer over a mask material layer, the patterned sacrificial layer having an etch selectivity different from that of the mask material layer; and performing an isotropic etch process to the mask material layer to form a mask layer by using the patterned sacrificial layer as an etch mask, a dimension of the mask layer being smaller than a dimension of the patterned sacrificial layer.
 2. The method for fabricating a mask of claim 1, wherein a method for forming the patterned sacrificial layer comprises: forming a sacrificial layer over the mask material layer; forming a patterned photoresist layer over the sacrificial layer; and etching the sacrificial layer by using the patterned photoresist layer as an etch mask.
 3. The method for fabricating a mask of claim 2, wherein the patterned photoresist layer has a critical dimension (CD), and the dimension of the mask layer is smaller than a CD.
 4. The method for fabricating a mask of claim 1, wherein the isotropic etch process comprises a wet etch process.
 5. The method for fabricating a mask of claim 1, wherein the mask material layer comprises a material selected from the group consisting of silicon oxide, silicon nitride, silicon oxynitride, polysilicon, doped polysilicon and a metal material.
 6. The method for fabricating a mask of claim 1, wherein the patterned sacrificial layer comprises a material selected from the group consisting of silicon oxide, silicon nitride, silicon oxynitride, polysilicon, doped polysilicon and a metal material.
 7. A patterning process, comprising: forming a mask material layer over a material layer, the mask material layer having an etch selectivity different from that of the material layer; forming a patterned sacrificial layer over the mask material layer, the patterned sacrificial layer having an etch selectivity different from that of the mask material layer, the patterned sacrificial layer having an etch selectivity the same as, or different from, that of the material layer; performing an isotropic etch process to the mask material layer to form a mask layer by using the patterned sacrificial layer as an etch mask, a dimension of the mask layer being smaller than a dimension of the patterned sacrificial layer; and etching the material layer by using the mask layer as an etch mask.
 8. The patterning process of claim 7, wherein a method for forming the patterned sacrificial layer comprises: forming a sacrificial layer over the mask material layer; forming a patterned photoresist layer over the sacrificial layer; and etching the sacrificial layer by using the patterned photoresist layer as an etch mask.
 9. The patterning process of claim 8, wherein the patterned photoresist layer has a critical dimension (CD), and the dimension of the mask layer is smaller than the CD.
 10. The patterning process of claim 7, wherein the isotropic etch process comprises a wet etch process.
 11. The patterning process of claim 7, wherein the mask material layer comprises a material selected from the group consisting of silicon oxide, silicon nitride, silicon oxynitride, polysilicon, doped polysilicon and a metal material.
 12. The patterning process of claim 7, wherein the patterned sacrificial layer comprises a material selected from the group consisting of silicon oxide, silicon nitride, silicon oxynitride, polysilicon, doped polysilicon and a metal material.
 13. The patterning process of claim 7, wherein the material layer comprises a material selected from the group consisting of silicon oxide, silicon nitride, silicon oxynitride, polysilicon, doped polysilicon and a metal material. 